This invention generally relates to treatment of atherosclerotic plaque, and particularly to treatment of vulnerable plaque using a balloon catheter.
Percutaneous transluminal coronary angioplasty (PTCA) is a widely used procedure for treating the occlusion of coronary vessels by atherosclerotic plaque. In PTCA procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of a dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with fluid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated vessel and the dilatation catheter can be removed therefrom. In such angioplasty procedures, there may be restenosis of the vessel, i.e. reformation of the arterial blockage from significant neointimal thickening relative to the vessel diameter, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant a stent inside the artery at the site of the lesion. Studies have shown correlations between vessel damage caused by PTCA and neointimal growth. See Schwartz et al., JACC, Vol. 19, No. 2: 267-74 (1992), incorporated by reference herein in its entirety.
In the design of catheter balloons, characteristics such as strength, compliance, and profile of the balloon are carefully tailored depending on the desired use of the balloon catheter, and the balloon material and manufacturing procedure are chosen to provide the desired balloon characteristics. A variety of polymeric materials are conventionally used in making catheter balloons. Use of polymeric materials such as polyethyleneterephthalate (PET) that do not stretch appreciably consequently necessitates that the balloon is first formed by blow molding, and then the deflated balloon material, in the form of deflated wings, are folded around the catheter shaft prior to introduction of the balloon into the patient's body lumen. However, it can be desirable to employ balloons that do not have deflated folded wings, but which instead can be expanded to the working diameter within the patient's body lumen from an essentially wingless, cylindrical or tubular shape which conforms to the catheter shaft. For example, catheter balloons have been described which are formed of expanded polytetrafluoroethylene (ePTFE) expanded in place within the patient's body lumen without blow-molding the ePTFE tubing. The ePTFE tubing is formed of a sheet of ePTFE wrapped on a mandrel and then heated to fuse the layers of wrapped material together, and the resulting tubular ePTFE balloon is bonded to a catheter-shaft.
A current therapeutic challenge is the treatment of unstable or vulnerable plaque. The term “vulnerable plaque” refers to an atherosclerotic plaque which may rupture and/or erode, with subsequent thrombosis, typically leading to acute myocardial infarction. In “stable” plaque, the lipid core or necrotic core is protected by a robust fibrous cap composed primarily of long chain extracellular matrix proteins (ECM) such as elastin and collagen. The strength of the fibrous cap is determined largely by ECM density, and especially the density of collagen. Various morphologic features have been associated with vulnerable plaque including thinned or eroded fibrous caps, lesion eccentricity, proximity of constituents having very different structural moduli, e.g., lipid and fibrous tissue, and the consistency and distribution of lipid accumulations. The most common type of vulnerable plaque, often called fibroatheroma, is a raised plaque beneath the innermost arterial layer (i.e., the intima), containing a large lipid core or a large necrotic core rich in lipids, cholesterol crystals, cholesterol esters, macrophages, and other cells, and having a fibrous cap which can become weakened. When ruptured, the luminal blood becomes exposed to highly thrombogenic core material, such as tissue factor (TF), which can result in total thrombotic occlusion of the artery. Due to the substantial danger posed by vulnerable plaque, it would be a significant advance to provide a method of treating such lesions.